Brannon Godfrey, a deputy city manager, said in an e-mail to city officials Friday that the man was in police custody on an unrelated case and confessed to setting the fire. The Fire Department identified him as Tyrone Donte Taylor of Portsmouth. He was being held in the Portsmouth jail without bond.

The fire was set about 6 p.m. in the book drop at the rear of the building and damaged the area near the book drop. But soot and ash spread through the building, and the library will be closed for at least 90 days for cleanup and repairs.